Changes in JNK1 activity in the frog (Rana esculenta) testis.

Several lines of evidences support a key role of mitogen-activated protein kinases (MAPK) in male fertility. It has been used as a non-mammalian vertebrate model, the frog Rana esculenta, to investigate the regulation of Jun amino-terminal kinase 1 (JNK1) activity in the testis in two different periods of the annual reproductive cycle: winter stasis and breeding season. JNK1 protein was localized by immunohistochemistry in the cytoplasm and nucleus of spermatogonia (SPG) and spermatocytes (SPC) during all the year. Immunoprecipitation analysis of JNK1 clearly shows that this isoform presents a strong phosphorylation status (thr183/Tyr185) in the breeding period, in contrast with only very low activity during the winter stasis. Simultaneously, during the breeding period c-Jun protein is highly phosphorylated on Ser-63. These data suggest that the increase of JNK1 activity, with strong c-Jun phosphorylation (Ser-63) during the breeding period, could be the signal of increasing transcriptional activity in the frog testis. Copyright 2003 Wiley-Liss, Inc.